Folger, now a KTM test rider alongside Dani Pedrosa and Mika Kallio, will step in from round three at COTA next month, marking his first MotoGP appearance since 2017 when he was a Tech3 Yamaha rookie.

The German took a podium finish at his home round that year before his premier-class career was suddenly cut short by illness.

After withdrawing from the final four rounds, Folger stepped back from MotoGP completely. He subsequently took part in Yamaha test riding duties and competed in the 2021 World Superbike series before signing on as an official KTM MotoGP test rider for 2023.

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"First of all I really hope Pol is doing well and getting back on his feet as soon as possible," said Folger, 29.

"I’m sure he has the right people around him. From my side I’m looking forward to racing again and arriving to Texas to see all the guys from my old team! I hope we can do a decent job and I know it will be a big challenge for me since testing has only just started.

"However, this will be a great opportunity to get up to speed and learn more about the bike. I’m thankful and now looking to Texas.”

Espargaro suffered jaw, back and lung injuries when he bounced through the gravel trap and into a trackside barrier during Friday practice at last weekend's Portimao season opener.

The Spaniard underwent surgery for his jaw fracture on Tuesday. He will 'remain under observation for a couple of days and is hopeful of being home soon when he’ll be able to step-up his physiotherapy and define a timeframe to get back in the saddle'.

“It’s clear Pol needs time to make a full recovery and our thoughts are still with him and we are in contact all the time," said Tech3 team manager Nicolas Goyon. who was also Folger's Tech3 crew chief during the 2017 MotoGP season.

"Until he is ready though, Jonas’ testing role together with his recent MotoGP experience meant he is the perfect fill-in. We had some good memories with him a few years ago and he tested with us in Sepang this pre-season. He’s a great guy and we’re delighted to welcome him back.”

Pedrosa is scheduled to make a KTM wild-card race appearance in round four, at Jerez in Spain.

Espargaro is one of four riders missing this weekend's Argentine round due to injury but Enea Bastianini (shoulder), Miguel Oliveira (leg) and Marc Marquez (hand) are all aiming to return at COTA.

MotoGP teams do not need to field a replacement until 10 days after their full-time rider is withdrawn, meaning there are no substitutes at Termas de Rio Hondo this weekend.